Signal to noise ratio in an OCT/confocal system and penetration depth in OCT

An OCT system is built around a confocal optical receiver by adding a reference beam to the beam returned from the target tissue to the photodetector. The amount of light collected by the OCT receiver (both signal and background signal) depends on the parameters of the confocal receiver. We are interested in a configuration that allows the simultaneous display of the confocal signal and the OCT signal, which requires a separate confocal channel in the system. In this case, the S/N performance is different in the two channels and depends on the optical configuration used. The paper discusses the noise sources in the two channels. S/N ratios are numerically evaluated for cases of experimental interest. As far as the penetration depth in OCT is concerned, a value of 20 optical depths was considered achievable in previous reports if only the shot noise was considered. We correct this value by taking into account the excess photon noise and the limitations imposed by the safety power limits. Multiple scattering determines an increase in noise via the excess photon noise term.